An invention of lifting a hood of a vehicle or a technology of disposing an airbag on the hood is proposed for decreasing an impact that is suffered by a head of a pedestrian when the vehicle collides with the pedestrian. In adopting the invention or technology, various adverse influences result from operating a protecting device on the hood (e.g., active hood) when a collision object is not a pedestrian.
For instance, when a vehicle collides with a light object that is not discriminated from a pedestrian, such as a triangle corn or a signboard indicating road construction, the protecting device is uselessly operated. This involves a useless repair cost. Further, by contrast, when a vehicle collides with a heavy stationary object that is not discriminated from a pedestrian, such as a concrete wall or another vehicle, a problem occurs that the hood being lifted is backed into an interior of the vehicle.
Accurately determining whether a collision object is a pedestrian is thereby more required than before, so that several methods for determining the collision object are proposed. For instance, a first method (Patent document 1) uses a collision load (or deformation amount), duration of the collision load, and a vehicle speed. A second method (Patent document 2) uses a deformation amount at a collision timing (corresponding to collision load), a time-series variation of the deformation amount, and a vehicle speed. In the two methods, a pedestrian is discriminated from other collision objects by setting a threshold in the load, variation amount, and time.
(Patent document 1: JP-H11-028994 A)
(Patent document 2 JP-H11-310095 A (U.S. Pat. No. 6,561,301 B1))
However, it was known that these methods that simply utilize collision load waveforms involve insufficient determination accuracy, resulting in insufficient reliability, regardless of a lot of workloads for experiments. Here, the experiments are required for specifying the threshold for the time and load (variation amount) with respect to each of various vehicle speeds.
Collision objects have individual shapes and rigidity. Even when each of the collision objects has an equal speed and an equal mass, a waveform of a collision load F (=ma) is thereby variable. As a result, a characteristic of the collision load waveform such as duration of the collision load, an increasing ratio, or a peak value cannot easily nor accurately discriminate a pedestrian from the other objects.